1. Field of the Invention
This invention relates to an abrasive article having a sheet-like structure having a major surface having deployed thereon a plurality of abrasive composites having precise shapes, wherein the precise shapes are not all identical. The invention also relates to methods of manufacturing an abrasive article, and a production tool used to manufacture such an abrasive article, and a method of using such an abrasive article to reduce a surface finish.
2. Discussion of the Art
In general, abrasive articles employ a plurality of abrasive particles which are bonded together as a unitary structure (e.g., a grinding wheel) or bonded separately to a common backing (e.g., a coated abrasive article). While these types of abrasive articles have been utilized to abrade and finish workpieces for many years, problems remain in the field.
For instance, one persistent problem confronting the abrasive industry arises from the generally inverse relationship associated between the cut rate (i.e., the amount of workpiece removed for a given time interval) and the finish that is imparted by the abrasive article on the workpiece surface. That is, it is difficult to design an abrasive article that affords a relatively high rate of cut while concomitantly imparting a relatively fine surface finish on the workpiece being abraded. This explains the presence of a wide range of abrasive products in the market using coarse grit (i.e., relatively large particle size of abrasive particles) to fine grit (i.e., relatively small particle size of abrasive particles). The use of these differently grit-sized abrasive products in a separate and sequential manner can provide some measure of success in ultimately achieving both a high cut and a fine finish, but the practice can be cumbersome and time consuming. Naturally, a single abrasive article which simultaneously would provide both high cut rate and fine finish would be more convenient and highly desired in the industry.
In addition to these goals, it has also been desired in the abrasive industry to provide an abrasive article which imparts a consistent surface finish in the workpiece while lessening or preventing scribing and/or chatter. Scribing refers to the occurrence of pronounced unwanted grooves in the workpiece surface which results in an increase in surface roughness units (Ra). Ra is the arithmetic average of the scratch depth. Typically, the grooves, when they occur, extend in the surface of the workpiece in a direction tracking the relative motion of the abrasive article vis-a-vis the workpiece surface. On the other hand, chatter means an undesirable repetive pattern created on the surface of a workpiece, usually at regular spaced intervals at a direction perpendicular to the direction of belt movement.
While various attempts have been made to create new and improved abrasive products, no complete solution to the problems noted above have been presented. While the following list of references describe a variety of abrasive products none is known to provide a completely satisfactory result to these problems.
More specifically, U.S. Pat. No. 2,115,897 (Wooddell et al.) teaches an abrasive article having a backing and attached thereto by an adhesive are a plurality of blocks of bonded abrasive material. These bonded abrasive blocks can be adhesively secured to the backing in a specified pattern.
U.S. Pat. No. 2,242,877 (Albertson) teaches a method of making a compressed abrasive disc. The method involves embedding abrasive particles in a binder layer that is coated on a fibrous backing. Then, a mold die is used to impart a molded pattern or contour into the thickness of binder and particle layer under heat and pressure to form a compressed abrasive disc. The molded surface of the abrasive disc has a specified working surface pattern which is the inverse of the profile of the molding die.
U.S. Pat. No. 2,755,607 (Haywood) teaches a coated abrasive in which there are land and groove abrasive portions, which can form, for example, an overall rectlinear or serpentine pattern. An adhesive coat is applied to the front surface of a backing and this adhesive coat is then combed to create peaks and valleys to pattern the surface of the adhesive coat. Haywood discloses that each of the lands and grooves formed in the adhesive coat by such a combing procedure preferably have the same width and thickness, but that they may be varied. Next the abrasive grains are distributed uniformly in the lands and grooves of the previously patterned adhesive coat followed by solidification of the adhesive coat. The abrasive particles used in Haywood are individual grains which are not used in slurry form with other grains in a binder. Therefore, the individual abrasive grains have irregular non-precise shapes.
U.S. Pat. No. 3,048,482 (Hurst) discloses an abrasive article comprising a backing, a bond system and abrasive granules that are secured to the backing by the bond system. The abrasive granules are a composite of abrasive grains and a binder which is separate from the bond system. The abrasive granules are three dimensional and are preferably pyramidal in shape. To make this abrasive article, the abrasive granules are first made via a molding process. Next, a backing is placed in a mold, followed by the bond system and the abrasive granules. The mold has patternized cavities therein which results in the abrasive granules having a specified pattern on the backing.
U.S. Pat. No. 3,605,349 (Anthon) pertains to a lapping type abrasive article. The binder and the abrasive grain are mixed together and then sprayed onto the backing through a grid. The presence of the grid results in a patterned abrasive coating.
Great Britain Patent Application No. 2,094,824 (Moore) pertains to a patterned lapping film. The abrasive slurry is prepared and the slurry is applied through a mask to form discrete islands. Next, the resin or binder is cured. The mask can be a silk screen, stencil, wire, or a mesh.
U.S. Pat. No. 4,644,703 (Kaczmarek et al.) concerns a lapping abrasive article comprising a backing and an abrasive coating adhered to the backing. The abrasive coating further comprises a suspension of lapping size abrasive grains and a binder cured by free radical polymerization. The abrasive coating can be shaped into a pattern by a rotogravure roll.
U.S. Pat. No. 4,773,920 (Chasman et al.) concerns a lapping abrasive article comprising a backing and an abrasive coating adhered to the backing. The abrasive coating comprises a suspension of lapping size abrasive grains and a binder cured by free radical polymerization. The abrasive coating can be shaped into a pattern by a rotogravure roll.
U.S. Pat. No. 4,930,266 (Calhoun et al.) teaches a patterned abrasive sheeting in which the abrasive granules are strongly bonded and lie substantially in a plane at a predetermined lateral spacing. In this invention the abrasive granules are applied via a impingement technique so that each granule is essentially individually applied to the abrasive backing. This results in an abrasive sheeting having a precisely controlled spacing of the abrasive granules.
U.S. Pat. No. 5,014,468 (Ravipati et al.) pertains to a lapping film intended for ophthalmic applications. The lapping film comprises a patterned surface coating of abrasive grains dispersed in a radiation cured adhesive binder. The patterned surface coating has a plurality of discrete raised three dimensional formations having widths which diminish in the direction away from the backing. To make the patterned surface, an abrasive slurry is applied to a rotogravure roll to provide a shapes surface which is then removed from the roll surface and then the radiation curable resin is cured.
U.S. Pat. No. 5,015,266 (Yamamoto) pertains to an abrasive sheet by uniformly coating an abrasive adhesive slurry over an embossed sheet. The resulting abrasive coating has high and low abrasive portions formed by the surface tension of the slurry, corresponding to the irregularities of the base sheet.
U.S. Pat. No. 5,107,626 (Mucci) teaches a method of providing a patterned surface on a substrate by abrading with a coated abrasive containing a plurality of precisely shaped abrasive composites. The abrasive composites are in a non-random array and the abrasive composites comprise a plurality of abrasive grains dispersed in a binder.
U.S. Pat. No. 5,152,917 (Pieper et al.) discloses a coated abrasive article that provides both a relatively high rate of cut and a relatively fine surface finish on the workpiece surface. The structured abrasive of Pieper et al. involves precisely shaped abrasive composites that are bonded to a backing in a regular nonrandom pattern. The consistency of the profile of the abrasive composites provided by the abrasive strucutre of Pieper et al., among other things, helps provide a consistent surface finish in the worked surface.
Japanese Patent Application No. S63-235942 published Mar. 23, 1990 teaches a method of a making a lapping film having a specified pattern. An abrasive slurry is coated into a network of indentations in a tool. A backing is then applied over the tool and the binder in the abrasive slurry is cured. Next, the resulting coated abrasive is removed from the tool. The binder can be cured by radiation energy or thermal energy.
Japanese Patent Application No. JP 4-159084 published Jun. 2, 1992 teaches a method of making a lapping tape. An abrasive slurry comprising abrasive grains and an electron beam curable resin is applied to the surface of an intaglio roll or indentation plate having a network of indentations. Then, the abrasive slurry is exposed to an electron beam which cures the binder and the resulting lapping tape is removed from the roll.
U.S. Ser. No. 07/820,155 filed Jan. 13, 1992 (Calhoun), which is commonly assigned to the owner of the present application, teaches a method of making an abrasive article. An abrasive slurry is coated into recesses of an embossed substrate. The resulting construction is laminated to a backing and the binder in the abrasive slurry is cured. The embossed substrate is removed and the abrasive slurry adheres to the backing.
U.S. Pat. No. 5,219,462 (Bruxvoort et al.) teaches a method for making an abrasive article. An abrasive slurry is coated substantially only into the recesses of an embossed backing. The abrasive slurry comprises a binder, abrasive grains and an expanding agent. After coating, the binder is cured and the expanding agent is activated. This causes the slurry to expand above the surface of the embossed backing.
U.S. Ser. No. 08/004,929 filed Jan. 14, 1993 (Spurgeon et al.), which is commonly assigned to the owner of the present application, teaches a method of making an abrasive article. In one aspect of this patent application, an abrasive slurry is coated into recesses of an embossed substrate. Radiation energy is transmitted through the embossed substrate and into the abrasive slurry to cure the binder.
U.S. Ser. No. 08/067,708 filed May 26, 1993 (Mucci et al.), which is commonly assigned to the owner of the present application, teaches a method of polishing a workpiece with a structured abrasive. The structured abrasive comprises a plurality of precisely shaped abrasive composites bonded to a backing. During polishing, the structured abrasive oscillates.
The use of variable pitch sawing teeth has been disclosed as a cutting edge for a hack saw blade, such as mentioned in a trade advertisement distributed by Lenox Co. and entitled "Lenox Hackmaster V Vari-Tooth Power Hack Saw Blades", to provide balanced cutting action and quiet performance. This hack saw blade design is described as useful to saw metal bar stock, ganged workpieces, or work with holes, slots or interruptions. This hack saw blade design is not specifically disclosed as adaptable for frictional abrasion applications between two rubbing surfaces including a complex three-dimensional working surface, nor does the LENOX publication disclose the wherewithal therefor.
Although some of the abrasive articles made according to the aforementioned patents, viz. Pieper et al., might provide an abrasive article yielding both high rate of cut and relatively fine finish, it has been observed that scribing can occur in surfaces worked by some prior art abrasive articles when the abrasive articles are used. For instance, many abrasive articles have directional limitations insofar as how the articles are to be oriented relative to the work surface to be reduced, i.e., some articles cannot be used omnidirectionally. If used improperly by accident or neglect, e.g., if such an abrasive article is not properly aligned with the surface to be worked by the operator, these abrasive articles, among other things, can cause scribing in the worked surface.
Therefore, it can be understood that the abrasive industry would highly value a versatile high-cut rate, fine finish abrasive article which is more resistant to inadvertent scribing and more adaptable to a wider range of abrasive conditions.